How do you do this problem?

[Twinklebunny]

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Hi..I'm sure this problem isn't that hard, but if someone could please explain to me how the answer is D I would appreciate it very much.

In watermelons, the unlinked genes for
green color (G) and for short length (S)
are dominant over alleles for striped color
(g) and long length (s). Predict the
phenotypes and their ratios for the cross
Ggss x ggSs.
A. All green short
B. 1:2:1 green short: striped long:
striped short
C. All striped long
D. 1:1:1:1 green short: striped short:
green long: striped long
E. 1:1 green short: striped long

 

[LuckMC11]

if you split the test crosses up, you would have 1 test cross of Gg x gg, and 1 of ss x Ss. now if you do the G test cross, you would get 2 Gg and 2 gg. for the S test cross, you would get 2 Ss and 2 ss.

so when you combine the different possibilities, you would end up with GgSs, ggSs, Ggss, ggss. (so 1 of each, giving 1:1:1:1 ratio)

hope this helps!

 

[Imanm]

Hi..I'm sure this problem isn't that hard, but if someone could please explain to me how the answer is D I would appreciate it very much.

In watermelons, the unlinked genes for
green color (G) and for short length (S)
are dominant over alleles for striped color
(g) and long length (s). Predict the
phenotypes and their ratios for the cross
Ggss x ggSs.
A. All green short
B. 1:2:1 green short: striped long:
striped short
C. All striped long
D. 1:1:1:1 green short: striped short:
green long: striped long
E. 1:1 green short: striped long

G is dominant over g so the genotype G- would give you the green phenotype.

S is dominant over s so the genotype S- would give you the Short watermelons.

You have a test cross with regards to each gene.(meaning half of the green water melones are short and also half of the striped are short, with the other halve being long) so D is the correct answer.

 

[UCB05]

Hi..I'm sure this problem isn't that hard, but if someone could please explain to me how the answer is D I would appreciate it very much.

In watermelons, the unlinked genes for
green color (G) and for short length (S)
are dominant over alleles for striped color
(g) and long length (s). Predict the
phenotypes and their ratios for the cross
Ggss x ggSs.
A. All green short
B. 1:2:1 green short: striped long:
striped short
C. All striped long
D. 1:1:1:1 green short: striped short:
green long: striped long
E. 1:1 green short: striped long

Your possible gametes for the two parents are:
(Gs, gs) x (gS, gs)

Therefore your possible offspring phenotypes from the coupling of a gamete from each parent are:
GgSs, Ggss, ggSs, ggss leading to each of the 4 possible phenotypes shown in answer D.

 

[Twinklebunny]

if you split the test crosses up, you would have 1 test cross of Gg x gg, and 1 of ss x Ss. now if you do the G test cross, you would get 2 Gg and 2 gg. for the S test cross, you would get 2 Ss and 2 ss.

so when you combine the different possibilities, you would end up with GgSs, ggSs, Ggss, ggss. (so 1 of each, giving 1:1:1:1 ratio)

hope this helps!

Hey guys,

Thanks for all the help. Regarding the method above, is this method safe to use when doing any Dihybrid cross problem? Because I have a hard time figuring out the gametes for the parents and the way you broke it up here makes sense to me.

 

[Troyvdg]

if you split the test crosses up, you would have 1 test cross of Gg x gg, and 1 of ss x Ss. now if you do the G test cross, you would get 2 Gg and 2 gg. for the S test cross, you would get 2 Ss and 2 ss.

so when you combine the different possibilities, you would end up with GgSs, ggSs, Ggss, ggss. (so 1 of each, giving 1:1:1:1 ratio)

hope this helps!

👍 just remember that unlinked genes always will occur in a 1:1:1:1 ratio if in a testcross (because they are all on different chromosomes and sort independently)

in a linked gene situation the ratio would be different because crossing over can occur because the genes are on the same chromosome

 

[Troyvdg]

Hey guys,

Thanks for all the help. Regarding the method above, is this method safe to use when doing any Dihybrid cross problem? Because I have a hard time figuring out the gametes for the parents and the way you broke it up here makes sense to me.

yes, its just a simplified punnett square. or you can use a diagram tree, which is a lot faster

 

[LuckMC11]

Hey guys,

Thanks for all the help. Regarding the method above, is this method safe to use when doing any Dihybrid cross problem? Because I have a hard time figuring out the gametes for the parents and the way you broke it up here makes sense to me.

yup its safe, used it in high school as well as in college. the dihybrid cross confuses me too and i think it would take too long to do over if u make 1 mistake in that large chart, and this way u can easily see the individual genotypes in the 2 smaller charts. and for this one, each test cross resulted in only 2 possibilities each, so it was even easier!

 

[Twinklebunny]

yes, its just a simplified punnett square. or you can use a diagram tree, which is a lot faster

I'm not familiar with tree diagrams dealing with genetics, it would be helpful if you could explain what they are in further detail. Thanks!